This invention relates to an immunogenic protein and cDNA which codes for said protein. More particularly, the invention is concerned with a surface membrane antigen of Entamoeba histolytica and a E. histolytica specific cDNA clone which encodes a serine rich E. histolytica protein.
The protozoan pathogen Entamoeba histolytica is a major cause of debilitating illness and death worldwide, infecting more than 500,000,000 people, and causing an estimated 50,000,000 cases of diarrhea, and 50,000 deaths yearly [Walsh in Aembiasis, Human Infection by Entamoeba histolytica, ed. Ravdin, J. I., John Wiley & Sons, Inc. New York, N.Y., pp. 93-105 (1988)]. There is an urgent need for a vaccine which could prevent the establishment of E. histolytica infection, or the development of invasive disease. Previous studies in animal models have demonstrated that immunity to E. histolytica infection can be produced by immunization with E. histolytica lysates [Ghadirian et al., Am. J. Trop. Med. Hyg. 29, 779-784 (1980); Krupp, Am. J. Trop. Med. Hyg. 23, 355-360 (1974); and Swartzwelder and Avant, Am. J. Trop. Med. Hyg. 567-575 (1952)]. However, the difficulty in obtaining large quantities of trophozoites, and the relatively crude nature of the immunizing preparations have severely limited the scope of these prior studies.
Recently, genomic differences between pathogenic and nonpathogenic E. histolytica have been reported by Tannich et al., Proc. Natl. Acad. Sci. USA 86, 5118-5122 (1989). These scientists utilized antibody screening and reported an amino acid sequence derived from a partial cDNA clone. No putative initiator methionine was found and no nucleotide data was reported by them. Nor are any tandem repeats or other characterization of the partial amino acid sequence provided by Tannich et al. No biological role for the Tannich et al protein is found in their report; instead, the paper is completely directed to the use of their partial cDNA clone to detect genomic differences between E. histolytica strains. However, Southern blotting with actin (a conserved protein, found in almost all organisms, and originally isolated by another scientific group) shows the same ability to differentiate between strains of E. histolytica as their probe, thereby suggesting that their probe is not unique in its ability to differentiate between E. histolytica strains.